Network system with seamless handover mechanism, operation method and control apparatus thereof

ABSTRACT

A network system based on a SDN with a seamless handover mechanism, an operation method and a control apparatus thereof are provided. The network system includes network devices, host devices and a control apparatus. The network devices are connected together. A part of the network devices are equipped with wireless access networks of the same SSID, and each of the host devices is connected to one of the network devices. The control apparatus is connected to the network devices. When a first host device of the host devices is changed to connect with a second network device from a first network device, the control apparatus controls the network devices to return an address resolution response packet to the first host device in response to an address resolution request packet transmitted from the first host device, so as to maintain an IP address of the first host device.

This application claims priority for Taiwan patent application no.105144051 filed on Dec. 30, 2016, the content of which is incorporatedby reference in its entirely.

FIELD OF THE INVENTION

The present invention relates to a software-defined network (SDN)-basednetwork system, an operation method and a control apparatus thereof,particularly to a network system with a seamless handover mechanism, anoperation method and a control apparatus thereof

BACKGROUND OF THE INVENTION

An ordinary network infrastructure includes a plurality of networkdevices connected together in a wired or wireless way. The wireless waymay be an Ad-hoc network mode, a mesh mode, or another mode. In thesituation of a wireless network, the network infrastructure includes aplurality of wireless access devices enabling the host devices to accessnetworks wirelessly. The wireless access devices may be also connectedwith the rear-end routers, transmitting the packets output by the hostdevices through the routers. In order to administer the networkconveniently, the administrator usually divides the network into manysubnetworks. The host device will connect with one subnetwork, using theInternet protocol address (IP address) of the subnetwork. While roamingto a new subnetwork, the host device must assume the IP address of thenew subnetwork for Internet access.

On the other side, a host device may turn from the original networkdevice to connect with a new network device. If the new network deviceand the original network device respectively belong to differentsubnetworks, a series of handover procedures must be undertaken to handover the host device to the new network device. The aforementionedhandover procedures include a Layer-3 handover operation. In the Layer-3handover operation, the host device maybe request a new IP address fromthe new network device to update the IP address and maintain the networkconnectivity.

An IP address had two functions. The first function is to act as thebasis of routing. In other words, while a host device moves to adifferent subnetwork, the IP address of the host device would change sothat the packets can be correctly transferred. The second function is toact as the endpoint identifier of the transport layer and theapplication layer. In the case of transmission control protocol (TCP)session, two sets of network sockets are used as the basis of networkconnection. A socket is formed by an IP address and a TCP port. Once theIP address or the TCP port of either socket set changes, the TCP sessionconnection would be interrupted.

Therefore, it is a target of the technicians in the field to provide anetwork system and a related operation method, which have a betterhandover mechanism, to achieve seamless handover and decrease the timespent in handover procedures.

SUMMARY OF THE INVENTION

The present invention provides an SDN-based network system with aseamless handover mechanism, an operation method and a control apparatusthereof, which have a better handover mechanism able to decrease thetime spent in handover procedures and reduce the probability of packetloss in handover procedures.

In one embodiment of the present invention, the present inventionprovides an SDN-based network system with a seamless handover mechanism.The network system comprises a plurality of network devices, a pluralityof host devices, and a control apparatus. The network devicesinterconnect to form a network infrastructure. A portion of the networkdevices provide a wireless network access function enabling the hostdevices to connect with the network devices in a wireless way. Thewireless access networks provided by a portion of network devices needan identical service set identifier (SSID). Each of the host devicesconnects one of the network devices through the wireless accessnetworks. The control apparatus connects with the network devices. Whilea first host devices of the host devices turns from a first networkdevice of the network devices to link with a second network device, thecontrol apparatus controls the network device to return the addressresolution response packet to the first host device corresponding to theaddress resolution request packet sent out by the first host device soas to maintain the IP (Internet Protocol) address of the first hostdevice.

In one embodiment of the present invention, the control apparatusestablishes a flow table of the network devices of the SDN-based networksystem and changes the flow entries in the flow table to dynamicallyadjust the transmission path of data packets or message packets, wherebyto maintain better transmission efficiency. The present invention doesnot adopt the anchor point device, such as that in PMIPv6, exempted fromestablishing network tunnels. The present invention uses the controlapparatus to arrange better paths.

In one embodiment of the present invention, the abovementioned networkdevices include an external-connection router device linking to externalnetworks. While the target IP address of a packet is an IP address of anexternal network, the network device transmits the packet to theexternal-connection router device, and the external-connection routerdevice transmits the packet to the external network.

In one embodiment of the present invention, while the abovementionedcontrol apparatus receives the address resolution request packet fromthe second network device, the control apparatus determines whether thesource IP address of the address resolution request packet is the IPaddress of the first host device. Alternatively, the control apparatusdetermines whether the source media access control (MAC) address of thepacket is the MAC address of the first host device. If the source IPaddress of the address resolution request packet is the IP address ofthe first host device or the source MAC address of the packet is the MACaddress of the first host device, the control apparatus determineswhether the target IP address, which is to be resolved, of the addressresolution request packet is the IP address of a network device or hostdevice of the first network. If the target IP address, which is to beresolved, in the address resolution request packet is the IP address ofa network device or host device of the first network, the controlapparatus finds out the MAC address corresponding to the target IPaddress that is to be resolved and places the found out MAC address inan address resolution response packet. Then, the control apparatusreturns the address resolution response packet to the first host devicethrough the second network device.

In one embodiment of the present invention, while the abovementionedcontrol apparatus receives another address resolution request packetthrough a first network device, the control apparatus determines whetherthe target IP address, which is to be resolved, of the another addressresolution request packet is the IP address of the first host device. Atthis time, the first host device may have roamed to a second network. Ifthe target IP address, which is to be resolved, of the another addressresolution request packet is the IP address of the first host device,the control apparatus places the MAC address of the first host device inanother address resolution response packet. The control apparatusreturns the another address resolution response packet to the hostdevice or network device in the first network through the first networkdevice.

In one embodiment of the present invention, while returning the addressresolution response packet to the first host device, the controlapparatus correspondingly updates the flow tables of all the networkdevices, whereby to guide all the packets going to the first host deviceto the first host device in the second network.

In one embodiment of the present invention, while returning anotheraddress resolution response packet to the first network, the controlapparatus correspondingly updates the flow tables of all the networkdevices, whereby to transmit the packets going to the first host deviceto the first host device having roamed to the second network.

One embodiment of the present invention provides an operation method ofa network system. The network system includes a plurality of networkdevices, a plurality of host devices and a control apparatus. Thenetwork devices interconnect in a wired or wireless way to form anetwork infrastructure. A portion of the network devices providewireless access networks. The wireless access networks have an identicalservice set identifier (SSID). Each of the host devices connects withone of the network devices providing wireless access networks throughthe wireless access networks. The control apparatus connects with thenetwork devices. The operation method comprises the following steps:while a first host device of the host devices turns from a first networkdevice of the network devices to connect with a second network device,the first host device sends out an address resolution request packet;corresponding to the address resolution request packet, the controlapparatus controls the network device to return an address resolutionresponse packet to the first host device, whereby to keep the IP addressof the first host device.

One embodiment of the present invention provides a control apparatusapplicable to a network system. The network system includes a pluralityof network devices and a plurality of host devices. The network devicesinterconnect. A portion of the network devices provide wireless accessnetworks. The wireless access networks have an identical service setidentifier (SSID). Each of the host devices connects with one of thenetwork devices providing wireless access networks through the wirelessaccess networks. The control apparatus includes a network unit and aprocessor. The network devices connect with the network unit. Theprocessor is coupled to the network unit. While a first host device ofthe host devices turns from a first network device of the networkdevices to connect with a second network device, the processor,corresponding to the address resolution request packet sent out by thefirst host device, controls the network device to return an addressresolution response packet to the first host device, whereby to keep theIP address of the first host device.

Based on the abovementioned technical schemes, the present inventionprovides a network system with a seamless handover mechanism, anoperation method and a control apparatus thereof, wherein the networksystem is programmed to make all the wireless access networks of thenetwork devices connecting with the network system have an identicalservice set identifier (SSID). While the host device is roaming amongwireless networks, the IP address of the host device must be unchangedbefore and after movement to maintain session continuity and achieveseamless handover. In one embodiment, while a host device turns from anoriginally-connected network device to connect with another networkdevice, the control apparatus, corresponding to the address resolutionrequest packet issued by the host device, controls the network device toreturn an address resolution response packet to the host device so as tomaintain the IP address of the host device.

Thus, the handover process undertaken by the host device is exemptedfrom the Layer-3 handover activity. Therefore, the time spent in thehandover process is decreased.

Below, embodiments are described in detail in cooperation with theattached drawings to make the characteristics and advantages of thepresent invention easily understood.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a network system according toone embodiment of the present invention;

FIG. 2 is a diagram schematically showing network devices according toone embodiment of the present invention;

FIG. 3 is a diagram schematically showing packet transmission accordingto one embodiment of the present invention;

FIG. 4 is a flowchart of an operation process of a network systemaccording to one embodiment of the present invention;

FIG. 5 is a diagram schematically showing operation of a network systemaccording to one embodiment of the present invention;

FIG. 6 is a flowchart of an operation method of a network systemaccording to one embodiment of the present invention;

FIG. 7 is a diagram schematically showing signal transmission of anetwork system according to one embodiment of the present invention; and

FIG. 8 is a diagram schematically showing signal transmission of anetwork system according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It should be explained beforehand for the numeral notations used in thespecification: the symbol “˜” is used to indicate a range, and thesymbol “-” is used between numbers to indicate a member of a group. Forexample, 120-1 is used to indicate that 120-1 is a first member of thegroup 120; 120-1˜120-4 is used to indicate a range of members in thegroup 120, including “120-1, 120-2, 120-3 and 120-4.

Refer to FIG. 1 a diagram schematically showing a network systemaccording to one embodiment of the present invention. The network system100 comprises a plurality of network devices 120-1˜120-4, a plurality ofhost devices 140-1˜140-2, and a control apparatus 160. The networkdevices 120-1˜120-4, the host devices 140-1˜140-2 and the controlapparatus 160 comprise hardware. The network devices 120-1˜120-4interconnect. Each of the host devices 140-1˜140-2 connects with one ofthe network devices 120-1˜120-4. In the embodiment shown in FIG. 1, thehost device 140-1 connects with the network device 120-2, and the hostdevice 140-2 connects with the network device 120-3. It should be noted:the host devices and the network devices are not limited to be thenetwork devices 120-1˜120-4 and the host devices 140-1˜140-2 of theembodiment shown in FIG. 1. In the present invention, the quantity ofthe host devices and the quantity of the network devices may beadoptable according to practical application.

In the embodiment shown in FIG. 1, the control apparatus 160 links tothe network devices 120-1˜120-4 through the network 180. The network 180is established by interconnecting a plurality of networks devices (notshown in the drawings). In the embodiment shown in FIG. 1, the controlapparatus 160 at least includes a network unit 162 and a processor 164.The network unit 162 is a communication device supporting variouswireless communication standards, such as Bluetooth, WiFi, WiMax, NFC(Near Field Communication), LTE (Long Term Evolution), and Wi-Fi. Theprocessor 164 is coupled to the network unit 162. The processor 164 maybe a system-on-chip (SOC), an application processor, a media processor,a microprocessor, a central processing unit (CPU), a digital signalprocessor, or the like. The network unit 162 links to the network 180.The network devices 120-1˜120-4 connect with the network unit 162through the network 180.

In the embodiment shown in FIG. 1, the network devices 120-1˜120-4 havea plurality of connection interfaces, such as routers, switches,wireless access points, gateways or servers, to realize the function ofrouting packets. However, the present invention does not limit that theconnection interfaces must be the abovementioned devices. In otherembodiments, the network devices 120-1˜120-4 are electronic deviceshaving a packet-routing function, such as personal digital assistants,smart mobile devices, notebooks, tablet computers or desktop computers.Further, the network devices 120-1˜120-4 may be a combination of theabovementioned devices, such as a combination of wireless access pointsand switches. However, the present invention neither limits that thenetwork device must be one of the abovementioned devices nor limit thatthe network devices must be a combination of the abovementioned devices.

It should be explained particularly: a portion of the network devices ofthe network system provide wireless access functions; another portion ofthe network devices do not provide wireless access functions. In detail,the network devices providing wireless access functions are locatedaround the periphery of the network, providing wireless access functionsfor the host devices intending to link with the network. On the otherside, the network devices purely used as router devices play the role ofthe network backbone and function to transfer packets. In the embodimentshown in FIG. 1, the network devices 120-2 and 120-3 can provide thewireless access functions and directly link with the host devices 140-1and 140-2 wirelessly. Alternatively, the network devices 120-2 and 120-3can indirectly link with the host devices 140-1 and 140-2 through otherwireless access devices providing wireless access functions. However,the present invention does not limit that the network devices shouldlink with the host devices directly or indirectly. In order to explainthe present invention clearly and concisely, the example will be used toexemplify the preset invention below: the network devices 120-1˜120-4provide wireless access functions, and the wireless access networksproviding the wireless access functions have an identical SSID. However,the present invention is not limited by the example.

Refer to FIG. 2 a diagram schematically showing the network devicesaccording to one embodiment of the present invention. In FIG. 2, each ofthe network devices 120-1˜120-4 has a first connection interface 122 a,a second connection interface 122 b and a third connection interface 122c. The first connection interface 122 a, the second connection interface122 b and the third connection interface 122 c are respectivelyconnection interfaces supporting various wireless communicationstandards and various wired communication standards.

In one embodiment, the interconnection of the network devices120-1˜120-4 is based on a first communication protocol. The firstcommunication protocol includes a Wi-Fi Direct (Wireless FidelityDirect) communication protocol. While the interconnection of the networkdevices 120-1 and 120-2 is based on the Wi-Fi Direct communicationprotocol, the second connection interface 122 b of the network device120-1 connects with the first connection interface 122 a of the networkdevice 120-2. In another embodiment, the first connection interface 122a of the network device 120-1 connects with the second connectioninterface 122 b of the network device 120-2. Herein, the firstconnection interface 122 a is the owner-end interface of the Wi-FiDirect communication protocol, and the second connection interface 122 bis the client-end interface of the Wi-Fi Direct communication protocol.It should be noted: the abovementioned first communication protocol isnot limited to be the Wi-Fi Direct communication protocol but may beanother communication protocol.

In one embodiment, the network devices 120-1˜120-4 include anexternal-connection router device. For example, the network device 120-4is an external-connection router device. The external-connection routerdevice (the network device 120-4) connects with external networks. Thehost devices 140-1˜140-2 are electronic devices able to link with thenetwork, such as personal digital assistants, smart mobile devices,notebooks, tablet computers or desktop computers. In this embodiment,each of the host devices 140-1˜140-2 can link with the network devices120-1˜120-4.

In one embodiment, the network devices 120-1˜120-4 provide wirelessaccess functions; the wireless access networks of the network devices120-1˜120-4, which the host devices 140-1˜140-2 link to, have anidentical SSID. In case of the host device 140-1 and the network device120-2 in FIG. 2, while linking to the network system 100 at the firsttime, the host device 140-1 links to the third connection interface 122c of the network device 120-2. The network device 120-2, which the hostdevice 140-1 links to, issues an IP address to the host device 140-1correspondingly. Alternatively, another network device, which links tothe network device 120-2, issues an IP address to the host device 140-1correspondingly.

In one embodiment, the control apparatus 160 is a control apparatus of asoftware-defined network (SDN) and links to the network devices120-1˜120-4 based on the Openflow Protocol. In other words, the network180 is a software-defined network. However, the present invention is notlimited by the embodiment. In the SDN environment, the processor 164 ofthe control apparatus 160 can dynamically adjust the transmission routesof data packets or message packets via setting the flow tables of thenetwork devices 120-1˜120-4 of the software-defined network and varyingthe flow entries of the flow tables, whereby to avoid network congestionand maintain transmission efficiency. In detail, the flow entry recordsthe related information of the packet (including the source IP address,the source MAC address, the target IP address, and the target MACaddress of the packet) and the corresponding operation rules. Accordingto the flow entries of the flow tables, the network devices 120-1˜120-4perform corresponding activities on the received packets, such astransferring the received packets to the host devices 140-1˜140-2 orother network devices 120-1˜120-4, or submitting the received packets tothe control apparatus 160. It should be noted: if the flow table doesnot have any operation rule corresponding to the packet received by oneof the network devices 120-1˜120-4, the network device will query thecontrol apparatus 160 through the network 180. In other words, thecontrol apparatus 160 sets a plurality of flow rules in the networkdevices 120-1˜120-4 for establishing the routes of transferring packets;the network devices 120-1˜120-4 look up the flow tables to determine howto transfer packets.

Refer to FIG. 3 a diagram schematically showing packet transmissionaccording to one embodiment of the present invention. In FIG. 3, whilethe host device 140-1 sends a packet to the host device 140-2, thesource IP address of the packet is the IP address of the host device140-1, and the target IP address of the packet is the IP address of thehost device 140-2. After receiving the packet through the thirdconnection interface 122 c, the network device 120-2 transfers thepacket through the second connection interface 122 b to the firstconnection interface 122 a of the network device 120-3 according to theflow table established in the control apparatus 160. The network device120-3 looks up the flow table and then transfers the packet through thethird connection interface 122 c to the host device 140-2.

In one embodiment, while the host device 140-2 sends a packet to thehost device 140-1, the source IP address of the packet is the IP addressof the host device 140-2, and the target IP address of the packet is theIP address of the host device 140-1. After receiving the packet throughthe third connection interface 122 c, the network device 120-3 transfersthe packet through the first connection interface 122 a to the secondconnection interface 122 b of the network device 120-2 according to theflow table. The network device 120-2 looks up the flow table and thentransfers the packet through the third connection interface 122 c to thehost device 140-1.

It should be noted: in one embodiment, if the interconnection of thenetwork devices 120-1˜120-4 is based on the Wi-Fi communication standardor the Wi-Fi Direct communication standard, the source MAC address ofthe packet varies with the device or connection interface, which sendsout or transfers the packet, in the transmission process, but the sourceIP address of the packet is maintained to be the IP address of theoriginal device issuing the packet. However, the present invention isnot limited by the embodiment. In one embodiment, suppose the firstconnection interface 122 a of the network device 120-3 and the secondconnection interface 122 b of the network device 120-2 work under theSTA (Station) mode of the Wi-Fi communication standard or the Wi-FiDirect communication standard; if the first connection interface 122 ais the owner-end interface and the second connection interface 122 b isthe client-end interface, the second connection interface 122 b onlyreceives the packet whose target MAC address is exactly the MAC addressof the second connection interface 122 b itself.

In the embodiment shown in FIG. 3, under the Wi-Fi communicationstandard or the Wi-Fi Direct communication standard, before the firstconnection interface 122 a of the network device 120-3 sends out thepacket, the target MAC address of the packet, which is corresponding tothe target IP address of the packet, needs to be modified to be the MACaddress of the second connection interface 122 b of the network device120-2. Contrarily, the first connection interface 122 a, which functionsas the owner-end interface, is free from the abovementioned limitationwhile receiving the packet. In other words, once all the firstconnection interfaces 122 a and second connection interfaces 122 b ofthe network devices 120-1˜120-4 work under the STA mode of the Wi-Ficommunication standard or the Wi-Fi Direct communication standard, theabovementioned rule of modifying the MAC address of the packet has toapply to all the network devices 120-1˜120-4.

Refer to FIG. 1 and FIG. 3 again. In the embodiment shown in FIG. 1 andFIG. 3, if the host device 140-1 issues a packet to a device in anexternal network, the target IP address of the packet is an IP addressof the external network. Because the network device 120-4 for connectionwith an external network, i.e. the external-connection router device, isnormally fixed, packet transmission will be done as long as the networkdevices 120-1˜120-4 can correctly guide the packet. After receiving thepacket, the network device 120-4 further transfers the packet to theexternal network. Similarly, while the target IP address of a packetfrom an external network is the IP address of the host device 140-1, thenetwork system 100 determines the network device that the host device140-1 links to, such as the network device 120-2. Then, packettransmission will be done correctly by the network devices 120-1˜120-4.

Under the abovementioned conditions, while the host device 140-1 or140-2 turns from the original network device to connect with anothernetwork device (for example, the host device 140-1 turns from thenetwork device 120-2 to connect with the network device 120-1), thenetwork system 100 can maintain the IP address of the host device 140-1or 140-2 unchanged via the assistance of the control apparatus 160,whereby to decrease the time consumed in the handover process and reducethe probability of packet loss.

FIG. 4 is a flowchart of the operation process of the network systemaccording to one embodiment of the present invention. FIG. 5 is adiagram schematically showing the operation of the network systemaccording to one embodiment of the present invention. Refer to FIG. 4and FIG. 5. While the host device 140-1 (a first host device) of thehost devices 140-1˜140-2 turns from the network device 120-2 (a firstnetwork device) of the network devices 120-1˜120-4 to connect with thenetwork device 120-1 (a second network device), the host device 140-1sends out an address resolution request packet (Step S210).Corresponding to the address resolution request packet sent out by thefirst host device 140-1, the processor 164 of the control apparatus 160controls the network devices 120-1˜120-4 to return an address resolutionresponse packet to the host device 140-1 so as to maintain the IPaddress of the host device 140-1 (Step S220).

The embodiment shown in FIGS. 1-5 is further used to demonstrate thepresent invention in detail. While the host device 140-1, whichoriginally connects with the network device 120-2, turns to connect withthe network device 120-1, i.e. while the host device 140-1 moves fromthe first network of the network device 120-2 to the second network ofthe network device 120-1, the host device 140-1 recognizes that theconnected object is changed and sends an address resolution requestpacket to the network device 120-2. In the embodiment, the addressresolution request packet is an ARP (Address Resolution Protocol)request packet. Ordinarily, an address resolution request packet canonly be transmitted in the Layer-2 network, such as a local area networkor the same subnetwork. The network device 120-1 and the network device120-2 are respectively located in different subnetworks. Hence, thenetwork device 120-1 will block the address resolution request packetunless the network device has been programmed specially. Thus, theaddress resolution request packet cannot be sent out. In such a case,the host device 140-1 will undertake a Layer-3 handover activity.However, if the network device 120-1 is an Openflow-based router devicein a software-defined network, the network device 120-1 is able to floodARP packets out, and it is possible for the host device 140-2 to receiveand response the ARP packet. However, whether the host device 140-2replies the ARP packet is a problem of probability. The presentinvention is to guarantee that the ARP packet can be replied correctly.

Refer to FIGS. 1-5. In the embodiment shown in FIGS. 1-5, while the hostdevice 140-1 turns from the network device 120-2 to connect with thenetwork device 120-1, the processor 164 of the control apparatus 160determines whether the host device 140-1 moves and links to a differentnetwork device according to the packet issued by the host device 140-1,e.g. whether the host device 140-1 turns from the network device 120-2to connect with the network device 120-1. Then, the network device120-1, which has received the address resolution request packet, can usethe Packet-In message of the OpenFlow protocol to package the addressresolution request packet and directly sends the address resolutionrequest packet to the control apparatus 160. The processor 164 of thecontrol apparatus 160 receives the address resolution request packetsent out by the host device 140-1 and determines whether the host device140-1 moves to a different subnetwork according to the addressresolution request packet. Next, corresponding to the address resolutionrequest packet, the processor 164 of the control apparatus 160 controlsthe network device 120-1 to return an address resolution response packetto the host device 140-1, whereby to maintain the IP address of the hostdevice 140-1. The abovementioned address resolution response packet isan ARP response packet. After receiving the address resolution responsepacket, the host device 140-1 would not undertake the Layer-3 handoveractivity but would stay in the original IP address. Thus, even thoughthe host device 140-1 turns from the network device 120-2 to connectwith the network device 120-1, the IP address of the host device 140-1would not change. Further, the technology that the control apparatus 160assists in returning the address resolution response packet alsoachieves an effect of the ARP Proxy, which can avoid the problem of ARPRequest Flooding that may occur in the cascaded network devices120-1˜120-4.

Refer to FIG. 6 a flowchart of an operation method of a network systemaccording to one embodiment of the present invention. Below, the presentinvention will be exemplified with the embodiment that the controlapparatus is used to determine whether the source IP address of theaddress resolution request packet is the IP address of the host deviceroaming to another subnetwork. However, the present invention is notlimited by the embodiment. In another embodiment, the control apparatusdetermines whether the source MAC address of the address resolutionrequest packet is the MAC address of the host device roaming to anothersubnetwork, whereby to learn which one of the host devices roams amongdifferent subnetworks. Refer to FIGS. 1-6 and related embodiments. Whilethe host device 140-1 turns from the network device 120-2 to connectwith the network device 120-1, i.e. the host device 140-1 moves from thefirst network of the network device 120-2 to the second network of thenetwork device 120-1, the host device 140-1, the network device 120-2 inthe first network or another host device in the first network sends outan address resolution request packet. It is particularly explainedherein: the first network of the network device 120-2 is a subnetwork ofthe network device 120-2, and the second network of the network device120-1 is a subnetwork of the network device 120-1.

Firstly, the network unit 162 of the control apparatus 160 receives theaddress resolution request packet through the network device 120-1 (StepS222). Next, the processor 164 of the control apparatus 160 determinesthe source IP address of the address resolution request packet. In theembodiment, before the host device 140-1 moves to the network device120-1, the control apparatus 160 has recorded the IP address of the hostdevice 140-1 when the host device 140-1 connects with the network device120-2 at the first time. Therefore, while the control apparatus 160receives the address resolution request packet corresponding to the factthat the host device 140-1 turns to connect with the network device120-1, the processor 164 of the control apparatus 160 determines whetherthe source IP address of the address resolution request packet is the IPaddress of the host device 140-1, which the control apparatus 160 hasrecorded (Step S224).

If the source IP address of the address resolution request packet is therecorded IP address of the host device 140-1, i.e. the determination ofStep S224 is yes, the processor 164 of the control apparatus 160determines whether the target IP address, which is to be resolved, ofthe address resolution request packet is one of the IP addresses of thenetwork device 120-2 and the host device 140-2 (Step S226). As mentionedabove, while the host device 140-1 turns from the network device 120-2to connect with the network device 120-1, the target IP address, whichis to be resolved in the address resolution request packet issued by thehost device 140-1, should be the network device 120-2. Therefore, if theprocessor 164 of the control apparatus 160 determines that the target IPaddress, which is to be resolved, of the address resolution requestpacket issued by the host device 140-1 is one of the IP addresses of thenetwork device 120-2 and the host device 140-2, i.e. the determinationof Step S226, is yes, the processor 164 of the control apparatus 160acquires the MAC address of the network device or host device, which iscorresponding to the target IP address that is to be resolved, andgenerates an address resolution response packet including theaforementioned MAC address (Step S228). For example, the processor 164of the control apparatus 160 acquires the MAC address of the networkdevice 120-2 and generates an address resolution response packetincluding the MAC address of the network device 120-2.

The network unit 162 of the control apparatus 160 returns the addressresolution response packet to the host device 140-1 through the networkdevice 120-1 (Step S230). For example, the control apparatus 160 usesthe Packet-Out message of the OpenFlow protocol to send the addressresolution response packet to the network device 120-1, and the networkdevice 120-1 further returns the address resolution response packet tothe host device 140-1. Thereby, after the host device 140-1 receives theaddress resolution response packet, the original IP address of the hostdevice 140-1 is maintained unchanged. The processor 164 of the controlapparatus 160 updates the flow tables of all the network devices120-1˜120-4 correspondingly (Step S232) so as to guide all the packetsgoing to the host device 140-1 to the host device 140-1 in the secondnetwork, whereby the transmission path of the host device 140-1 is keptup in the network system 100. It should be noted: in the embodiment, ifthe processor 164 of the control apparatus 160 determines that thetarget IP address, which is to be resolved, of the address resolutionrequest packet is neither the IP address of the network device 120-2 northe IP address of the host device 140-2, i.e. the determination of StepS226 is no, none address resolution response packet will be returned,and the process of the operation method is ended. On the other hand, ifthe processor 164 of the control apparatus 160 determines that thesource IP address of the address resolution request packet is not the IPaddress of the host device 140-1, i.e. the determination of Step S224 isno, the processor 164 of the control apparatus 160 further determineswhether the target IP address, which is to be resolved, of the addressresolution request packet is the IP address of the first host device140-1 (Step S234), whereby to process the address resolution requestsmade by other host devices in the first network to query about the hostdevice 140-1 having roamed to the second network. If the determinationof Step S234 is no, none address resolution response packet will bereturned, and the process of the operation method corresponding to thehost device 140-1 is ended.

If the target IP address, which is to be resolved, of the addressresolution request packet is the IP address of the first host device140-1, i.e. the determination of Step S234 is yes, the processor 164 ofthe control apparatus 160 takes the place of the host device 140-1 toreturn the address resolution response packet to the first network (StepS236). Further, the processor 164 of the control apparatus 160correspondingly updates the flow tables of all the network devices120-1˜120-4 (Step S238), whereby to maintain the transmission pathsbetween the host device 140-1 and the other network host devices in thefirst network of the network system 100.

Refer to FIG. 6. The network unit 162 of the control apparatus 160receives the address resolution request packet through the networkdevice 120-1 (Step S222), and the processor 164 of the control apparatus160 determines whether the address resolution request packet is sent outby the first host device. As mentioned above, in the embodiment, thehost device 140-1 turns from the network device 120-2 to connect withthe network device 120-1 and thus moves from the subnetwork of thenetwork device 120-2 to the subnetwork of the network deice 120-1.Therefore, it is in fact to determine whether the source IP address ofthe address resolution request packet is the IP address of the hostdevice 140-1 (Step S224).

Then, the network unit 162 of the control apparatus 160 returns theaddress resolution response packet to the host device 140-1 through thenetwork device 120-1 (Step S230). The processor 164 of the controlapparatus 160 correspondingly updates the flow tables of all the networkdevices 120-1˜120-4 (Step S232), whereby to maintain the transmissionpath of the host device 140-1 in the network system 100. According tothe above description, the control apparatus 160 determines whether thehost device 140-1 moves via observing the source MAC address issued bythe host device 140-1. Therefore, the control apparatus 160 can detectthe movement of the host device 140-1, neither unpacking the packet norcomparing IP addresses. The control apparatus 160 will generate the ARPresponse and directly transmit the ARP response to the host device 140-1through the new subnetwork. Corresponding to reception of the ARPresponse, the host device 140-1 would not undertake the Layer-3 handoveractivity but continues using the original IP address to maintain the TPCnetwork connection. Thus, it is unnecessary to transmit the succeedingpackets through the subnetwork used previously. The control apparatus160 can dynamically arrange the optimized or shortest route for packets.

FIG. 7 is a diagram schematically showing the signal transmission of thenetwork system according to one embodiment of the present invention.Refer to FIGS. 1-7. In the network system 100, while the host device140-1 connects with the network device 120-2 of the network system 100at the first time (Step S701), the control apparatus 160 uses the firstpacket sent out by the host device 140-1 to the network device 120-2 toverify the existence of the host device 140-1 (Step S703). On the otherhand, the host device 140-2 connects with the network device 120-3 (StepS702).

Suppose that host device 140-1 intends to communicate with the hostdevice 140-2 and that the host device 140-1 and the host device 140-2are located in the same subnetwork. The host device 140-1 sends anaddress resolution request packet ARP Req to the network device 120-2.The target IP address, which is to be resolved, of the addressresolution request packet is the IP address of the host device 140-2.The control apparatus 160 receives the address resolution request packetARP Req through the network device 120-2 (Step S705). As the host device140-1 connects with the network system 100 for the first time, thecontrol apparatus 160 controls the network device 120-2 to return anaddress resolution response packet ARP Res (Step S707). If the hostdevice 140-1 and the host device 140-2 are respectively located indifferent subnetworks, the process is free of the abovementioned step.

After the host device 140-1 has connected with the network system 100,the host device 140-1 can transfer packets to the other host devices,such as the host device 140-2. Herein, the host device 140-1 undertakesthe PING process with the host device 140-2 being the target. In theembodiment, the host device 160 undertakes the PING process to send anInternet control message request packet to the host device 140-2according to the lookup table in the address resolution response packetARP Res. The abovementioned Internet control message request packet isan ICMP (Internet Control Message Protocol) request packet.

The network device 120-2 and the control apparatus 160 receive theInternet control message request packet ICMP Req sent out by the hostdevice 140-1 (Step S709). After receiving the abovementioned Internetcontrol message request packet ICMP Req, the control apparatus 160 setsthe transmission route between the host device 140-1 and the host device140-2 correspondingly (Step S711). In the embodiment, setting thetransmission route includes updating the flow tables of the networkdevices 120-2 and the 120-3.

Next, the control apparatus 160 instructs the network device 120-2 totransmit the Internet control message request packet ICMP Req (StepS713). The network device 120-2 transmits the Internet control messagerequest packet ICMP Req to the network device 120-3 (Step S715). Thenetwork device 120-3 further transmits the Internet control messagerequest packet ICMP Req to the host device 140-2 (Step S717). Afterreceiving the Internet control message request packet ICMP Req, the hostdevice 140-2 returns an Internet control message response packetcorrespondingly. The Internet control message response packet is an ICMP(Internet Control Message Protocol) response packet.

In detail, the host device 140-2 transmits the Internet control messageresponse packet ICMP Res to the network device 120-3 (Step S719), andthe network device 120-3 transmits the Internet control message responsepacket ICMP Res to the network device 120-2 (Step S721). The networkdevice 120-2 further transmits the Internet control message responsepacket ICMP Res to the host device 140-1 (Step S723). Thus, the PINGprocess, which the host device 140-1 performs on the host device 140-2,is completed.

After a period of time, while the host device 140-2 turns to connectwith the network device 120-1 (Step S725), the host device 140-2 usesthe IP address of the network device 120-3 as the target IP address thatis to be resolved and transmits an address resolution request packet ARPReq to enable the control apparatus 160 to determine whether the hostdevice 140-2 is still in the original subnetwork. The network device120-1 and the control apparatus 160 receive the abovementioned addressresolution request packet ARP Req (Step S727). According to the IPaddress and MAC address of the network device 120-3, the controlapparatus 160 generates an address resolution response packet ARP Resand controls the network device 120-1 to return the address resolutionresponse packet ARP Res (Step S729), so as to maintain the IP address ofthe host device 140-2. Next, the control apparatus 160 updates the flowtables of the network devices 120-1˜120-4 (Step S731).

After the abovementioned handover activity has been completed, and whilethe host device 140-1 undertakes a PING process with the host device140-2 being the target, the Internet control message request packet ICMPReq and the Internet control message response packet ICMP Res aretransmitted by the network devices 120-1 and 120-2 (Steps S733, S735,S737, S739, S741 and S743). In detail, after the host device 140-2moves, the control apparatus 160 generates and returns the addressresolution response packet ARP Res to make the host device 140-2 deemthat it is still under the original network device 120-3, whereby tokeep the original IP address of the host device 140-2. Besides, the flowtables are modified to correct the target MAC addresses of packets,whereby to prevent the network devices from discarding the packetslabelled as the packets of different subnetworks, and whereby toguarantee that packets can be correctly transmitted.

FIG. 8 is a diagram schematically showing the signal transmission of thenetwork system according to another embodiment of the present invention.The embodiment shown in FIG. 8 is different from the embodiment shown inFIG. 7 in that FIG. 8 illustrates the signal transmission between thedevices of external networks and the host device 140-1. Refer to FIGS.1-8. In the embodiment, the host device 140-1 connects with the networkdevice 120-2 (Step S801). The control apparatus 160 uses the firstpacket transmitted by the host device 140-1 to the network device 120-2to verify the existence of the host device 140-1 (Step S803). If thehost device 140-1 connects with the network device 120-2 for the firsttime, the address resolution request packet ARP Req and the addressresolution response packet ARP Res are required for acquiring the IPaddress. However, the process that has been described above will notrepeat herein.

After connecting with the network system 100, the host device 140-1 canalso transmit packets to an arbitrary device of the external network.For example, the host device 140-1 undertakes a PING process with anarbitrary device in the external network being the target. In theembodiment, the host device 140-1 sends an Internet control messagerequest packet to an arbitrary device in the external network toundertake a PING process. The abovementioned Internet control messagerequest packet is an ICMP (Internet control message protocol) requestpacket.

In the embodiment, the network device 120-4 connects with an externalnetwork. If the host device 140-1 intends to perform a PING process on ahost device in the external device, the host device 140-1 sends out anInternet control message request packet ICMP Req, and the network device120-2 and the control apparatus 160 receive the Internet control messagerequest packet ICMP Req (Step S805). After receiving the Internetcontrol message request packet ICMP Req, the control apparatus 160 setsthe transmission path between the host device 140-1 and the networkdevice 120-4 correspondingly (Step S807). For example, the controlapparatus 160 updates the flow table of the network device 120-2.

Next, the control apparatus 160 instructs the network device 120-2 totransmit the Internet control message request packet ICMP Req (StepS809). The network device 120-2 transmits the Internet control messagerequest packet ICMP Req to the network device 120-3 (Step S811), and thenetwork device 120-3 further transmits the Internet control messagerequest packet ICMP Req to the network device 120-4 (Step S813). Afterreceiving the Internet control message request packet ICMP Req, thenetwork device 120-4 transmits the Internet control message requestpacket ICMP Req to a device in the external network (Step S815).

After receiving the Internet control message request packet ICMP Req,the device in the external network returns an Internet control messageresponse packet correspondingly. The Internet control message responsepacket is an ICMP (Internet Control Message Protocol) response packet.In detail, the external network sends the Internet control messageresponse packet ICMP Res to the network device 120-4 (Step S817); thenetwork device 120-4 sends the Internet control message response packetICMP Res to the network device 120-3 (Step S819); the network device120-3 sends the Internet control message response packet ICMP Res to thenetwork device 120-2 (Step S821); the network device 120-2 sends theInternet control message response packet ICMP Res to the host device140-1 (Step S823). Thus, the PING process, which the host device 140-1performs on an arbitrary device in the external network, is completed.

After a period of time, while the host device 140-1 turns to connectwith the network device 120-1 (Step S825), the host device 140-1 usesthe IP address of the network device 120-2 as the target IP address thatis to be resolved and transmits an address resolution request packet ARPReq according to the target IP address. The network device 120-1 and thecontrol apparatus 160 receive the address resolution request packet ARPReq (Step S827). The control apparatus 160 generates an addressresolution response packet ARP Res according to the IP address and MACaddress of the network device 120-2 and controls the network device120-1 to return the address resolution response packet ARP Res (StepS829), whereby the host device 140-1 still uses the original IP address.The control apparatus 160 can determine when to modify the flow tablesof the network devices 120-1, 120-2, 120-3, and 120-4. The controlapparatus 160 may modify the flow tables when new traffic appears.Alternatively, the control apparatus 160 immediately modifies the flowtables after the address resolution response packet ARP Res is completedand when the host device 140-1 is currently communicating with the otherhost devices. While the host device 140-1 undertakes a PING process withan arbitrary device as the target after the abovementioned handoverprocess is completed, the host device 140-1 sends an Internet controlmessage request packet ICMP Req, and the network device 120-1 and thecontrol apparatus 160 receive the Internet control message requestpacket ICMP Req (Step S831). The control apparatus 160 updates the flowtables of all the network devices 120-1, 120-2, 120-3 and 120-4 in theroute (Step S833) and instructs the network devices 120-1, 120-2, 120-3and 120-4 to transmit the Internet control message request packet ICMPReq (Step S835). Next, the Internet control message request packet ICMPReq and the Internet control message response packet ICMP Res aretransmitted by the network devices 120-1, 120-2, 120-3 and 120-4 (StepsS837, S839, S841, S843, S845, S847, S849, S851, S853, and S857).

In conclusion, the present invention provides a network system with aseamless handover mechanism, an operation method and a control apparatusthereof, wherein the network system is programmed to make all thewireless access networks have an identical service set identifier(SSID), and wherein the form of the backbone of the network system isnot particularly limited. While a host device turns from theoriginally-connected network device to connect with another networkdevice, the control apparatus controls the network device to return anaddress resolution response packet to a first host device correspondingto the address resolution request packet issued by the abovementionedhost device, whereby to keep the IP address of the first host device.Thereby, the handover process undertaken by the host device is exemptedfrom the Layer-3 handover operation. Thus, the time spent in handoverprocedures is decreased, and the probability of packet loss in handoverprocedures is lowered.

The present invention has been demonstrated above with the embodiments.However, these embodiments are only to exemplify the present inventionbut not to limit the scope of the present invention. Any person skilledin the art should be able to modify or vary the embodiments easilywithout departing from the scope of the present invention, which isbased on the claims stated below.

What is claimed is:
 1. A network system with a seamless handovermechanism, comprising: a plurality of network devices based on asoftware-defined network (SDN), and said network devices interconnect,and a portion of said network devices provide wireless access networks,and said wireless access networks have an identical service setidentifier (SSID); a plurality of host devices each connecting with oneof said network devices providing said wireless access networks; and acontrol apparatus connecting with said network devices, and while afirst host device of said host devices turns from a first network deviceof said network devices to connect with a second network device andmoves from a first network of said first network device to a secondnetwork of said second network device, said control apparatus controlssaid network devices to return an address resolution response packet tosaid first host device corresponding to an address resolution requestpacket issued by said first host device to keep an Internet protocol(IP) address of said first host device; wherein while said controlapparatus receives said address resolution request packet from saidsecond network device, said control apparatus determines whether asource media access control (MAC) address or a source IP address of saidaddress resolution request packet is an MAC address of said first hostdevice or an IP address of said first host device; when said source MACaddress of said address resolution request packet is said MAC address ofsaid first host device or said source IP address of said addressresolution request packet is said IP address of said first host device,said control apparatus determines whether a target IP address, which isto be resolved, of said address resolution request packet is an IPaddress of one of network devices and host devices in said firstnetwork; and when said target IP address, which is to be resolved, ofsaid address resolution request packet is said IP address of one of saidnetwork devices and said host devices in said first network, saidcontrol apparatus acquires an MAC address corresponding to said targetIP address, which is to be resolved, of said address resolution requestpacket and generates said address resolution response packet of said MACaddress, and said control apparatus returns said address resolutionresponse packet to said first host device through said second networkdevice.
 2. The network system according to claim 1, wherein said networkdevices include an external-connection router device connecting with anexternal network, and wherein while a target IP address of a packetbelongs to an IP address of said external network, said network devicestransmit said packet to said external-connection router device, and saidexternal-connection router device transmits said packet to said externalnetwork.
 3. The network system according to claim 1, wherein afterreturning said address resolution response packet to said first hostdevice, said control apparatus updates flow tables of said networkdevices to guide all packets going to said first host device to saidfirst host device in said second network.
 4. The network systemaccording to claim 1, wherein while said control apparatus receivesanother address resolution request packet through said first networkdevice, said control apparatus determines whether a target IP address,which is to be resolved, of said another address resolution requestpacket is said IP address of said first host device; and when saidtarget IP address, which is to be resolved, of said another addressresolution request packet is said IP address of said first host device,said control apparatus places an MAC address of said first host devicein another address resolution response packet and returns said anotheraddress resolution response packet through said first network device. 5.The network system according to claim 4, wherein after returning saidanother address resolution response packet to said first network, saidcontrol apparatus correspondingly updates flow tables of all saidnetwork devices to guide all packets going to said first host device tosaid first host device in said second network.
 6. An operation method ofa network system, wherein said network system includes a plurality ofnetwork devices based on a software-defined network (SDN), a pluralityof host devices and a control apparatus, and said network devicesinterconnect, and a portion of said network devices provide wirelessaccess networks, and said wireless access networks have an identicalservice set identifier (SSID), and each of said host devices connectswith one of said network devices providing said wireless accessnetworks, and said control apparatus connects with said network devices,and said operation method comprises: while a first host device of saidhost devices turns from a first network device of said network devicesto connect with a second network device and moves from a first networkof said first network device to a second network of said second networkdevice, said first host device sends out an address resolution requestpacket; and corresponding to said address resolution request packet,said control apparatus controls said network devices to return anaddress resolution response packet to said first host device to keep anIP address of said first host device; wherein said step of controllingsaid network devices to return said address resolution response packetto said first host device to keep said IP address of said first hostdevice further comprises steps: said control apparatus receiving saidaddress resolution request packet through said second network device;said control apparatus determining whether a source media access control(MAC) address or a source IP address of said address resolution requestpacket is an MAC address of said first host device or an IP address ofsaid first host device; if said source MAC address of said addressresolution request packet is said MAC address of said first host deviceor said source IP address of said address resolution request packet issaid IP address of said first host device, said control apparatusdetermining whether a target IP address, which is to be resolved, ofsaid address resolution request packet is an IP address of one ofnetwork devices and host devices in said first network; if said targetIP address, which is to be resolved, of said address resolution requestpacket is said IP address of one of said network devices and said hostdevices in said first network, said control apparatus acquiring an MACaddress corresponding to said target IP address, which is to beresolved, of said address resolution request packet and generating saidaddress resolution response packet of said MAC address; and said controlapparatus returning said address resolution response packet to saidfirst host device through said second network device.
 7. The operationmethod according to claim 6, further comprising: after returning saidaddress resolution response packet to said first host device, saidcontrol apparatus updating flow tables of said network devices to guideall packets going to said first host device to said first host device insaid second network.
 8. The operation method according to claim 6,further comprising: said control apparatus receiving another addressresolution request packet through said first network device; saidcontrol apparatus determining whether a target IP address, which is tobe resolved, of said another address resolution request packet is saidIP address of said first host device; and if said target IP address,which is to be resolved, of said another address resolution requestpacket, is said IP address of said first host device, said controlapparatus placing an MAC address of said first host device in anotheraddress resolution response packet and returning said another addressresolution response packet through said first network device.
 9. Theoperation method according to claim 8, wherein after returning saidanother address resolution response packet to said first network, saidcontrol apparatus correspondingly updating flow tables of all saidnetwork devices to guide all packets going to said first host device tosaid first host device in said second network.
 10. A control apparatusapplicable to a network system, and said network system includes aplurality of network devices based on a software-defined network (SDN)and a plurality of host devices, and said network devices interconnect,and a portion of said network devices provide wireless access networks,and said wireless access networks have an identical service setidentifier (SSID), and each of said host devices connects with one ofsaid network devices providing said wireless access networks, and saidcontrol apparatus comprises a network unit connecting with said networkdevices; and a processor coupled to said network unit, wherein while afirst host device of said host devices turns from a first network deviceof said network devices to connect with a second network device andmoves from a first network of said first network device to a secondnetwork of said second network device, said control apparatus controlssaid network devices to return an address resolution response packet tosaid first host device corresponding to an address resolution requestpacket issued by said first host device to keep an Internet protocol(IP) address of said first host device; wherein while said controlapparatus receives said address resolution request packet from saidsecond network device, said control apparatus determines whether asource media access control (MAC) address or a source IP address of saidaddress resolution request packet is an MAC address of said first hostdevice or an IP address of said first host device; when said source MACaddress of said address resolution request packet is said MAC address ofsaid first host device or said source IP address of said addressresolution request packet is said IP address of said first host device,said control apparatus determines whether a target IP address, which isto be resolved, of said address resolution request packet is an IPaddress of one of network devices and host devices in said firstnetwork; and when said target IP address, which is to be resolved, ofsaid address resolution request packet is said IP address of one of saidnetwork devices and said host devices in said first network, saidcontrol apparatus acquires an MAC address corresponding to said targetIP address, which is to be resolved, of said address resolution requestpacket and generates said address resolution response packet of said MACaddress, and said control apparatus returns said address resolutionresponse packet to said first host device through said second networkdevice.